The United States has condemned the “senseless” violence that left at least 31 people dead in south-west of Ukraine on Friday.
Dozens of people were killed by a fire at a building that pro-Russians had taken over in the port city of Odessa.
A blaze engulfed the building after running battles between pro-Kiev groups and separatists in the city.
Officials said some people were overwhelmed by smoke and others died after they jumped from the building.
The US called said the violence was “unacceptable” and urged all sides to work together to restore law and order in light of the “tragedy.
“The violence and mayhem that led to so many senseless deaths and injuries is unacceptable,” the state department said in a statement.
It also called on the Ukrainian authorities “to bring all those responsible to justice.”
Investigation underway
Ukraine’s interior ministry said the fire broke out in Odessa’s Trade Unions House but it did not give details of how the blaze started.
The exact sequence of events is still unclear, but reports suggest the separatists had barricaded themselves inside the building and both sides were throwing petrol bombs.
Ukrainian Deputy Foreign Minister Danylo Lubkivsky told the BBC that an investigation was under way into the events but insisted Russia was behind the violence.
“The situation remains under control. But the security situation is threatened by Russian special agents,” he said.
“That’s why we are requesting and demanding Russian authorities to stop their efforts that can undermine regional security and stability.”
Earlier on Friday four people were killed in clashes between the pro-Russian and pro-Kiev protesters in Odessa – the first such eruption of violence in the south after weeks of mounting unrest in Ukraine’s east.